Given: I have multiple already existing items of a specific template across my content tree. Template has some field that I want to update with a new value for all existing items, within some node I can specify.

Use cases for that scenario are really universal - you may use that for various purposes. What comes into my head, at a first glance, is the situation when you would like to assign some template to a workflow but already have multiple existing items of that template (just to remind - setting a field value at Standard Values will apply for all new, but not existing items of that particular template). In that case you need assign a workflow to each existing item individually.

Another good example is when you have a folder with multiple items, growing in amount with time flow. Then you may decide to make a folder bucketable, but those existing items require to set a Bucketable checkbox for each existing item individually. I have described that case in one of my previous blog posts - "Understanding Buckets: adding new items to buckets correctly". So let's pick up second case and try to solve it.

Solution: So, what are possible ways of achieving that goal? Not so much of them, there are just two options.

1. Straightforward option - use C# code. With C# task may be achieved by a recursive method, that accepts an item, verifies if the one is of desired template and if yes - updates the field and does the same for all item's children if any. Here is an example of such method and example of call :

The code above works out perfectly and does exactly what we want from it, however there are certain disadvantages: first of all you need to run the code in some context - call if from some existing class, for example. Second - as that is C# code - it must be re-compiled and re-deployed. And if you may need to amend small change into the code - will have to re-compile and re-deploy again. But, luckily, there is a much better and faster alternative:

2. PowerShell Module. That module integrates into the platform and offers unprecedentedly ultimate possibilities and power over Sitecore instance and databases. After installation there is PowerShell console and more advanced PowerShell ISE, where you may create and test scripts. They are executed immediately without any of prerequisites like rebuilt DLL with a code at your bin folder. So, here is a script that does exactly the same as previous C# code: